JP2013046014A - Adhesive for solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a connection body which can be connected in a short time while minimizing increase in connection resistance due to aggregation, and to provide a production method of the connection body, and a solar cell module including the connection body.SOLUTION: A curable adhesive containing conductive particles and an organic binder and electrically connecting a surface electrode conductive wiring and a tab line of a solar cell contains 0.01-1.6 vol% of conductive particles, and the content ratio of the conductive particles of 1 μm or less is 0.1-50 vol%.

Description

  The present invention relates to a curable adhesive for electrically connecting a surface electrode conductive wire and a tab wire of a solar battery cell, and electrically curing the surface electrode conductive wire and the tab wire by curing the curable adhesive. The present invention relates to a connecting body for connected solar battery cells, a solar battery module including the connecting body, and a method for producing the adhesive.

  The solar cell module usually has a structure in which a plurality of solar cells are connected in series and / or in parallel via tab wires (wiring members) electrically connected to the surface electrodes. Generally, a paste containing silver is used for the surface electrode of the solar battery cell, and a material mainly composed of a copper component is used for the tab wire.

  Conventionally, solder has been used to connect the surface electrode of the solar battery cell and the tab wire when the solar battery module is manufactured. Solder is widely used because it is excellent in connection reliability such as electrical conductivity and fixing strength, is inexpensive and versatile.

  On the other hand, in Patent Documents 1 and 2, in order to prevent the member such as the semiconductor structure in the solar cell from being heated and / or the influence of the solder volume shrinkage on the semiconductor structure or the like, the conductive material is used instead of the solder. A wiring connection method using a conductive adhesive film is disclosed.

JP 2007-158302 A JP 2011-49612 A

  In the connection method using the conductive adhesive film as shown in Patent Documents 1 and 2, adverse effects on the solar battery cells that occur when solder is used can be suppressed to some extent. However, in the case of a solar cell module used in a harsh environment, there is a problem that a connection portion is cracked due to expansion and contraction due to thermal history, and connection reliability is low.

  Moreover, as described in Patent Document 1, it is generally considered to use conductive particles having an average particle diameter of about 10 μm to 20 μm at about 5% by volume for the conductive adhesive film used for such applications. ing. However, when such relatively large particles are used in such amounts, a large amount of adhesive is required to fill the conductive particles. Therefore, it takes time to cure the adhesive, and it is difficult to bond in a short time.

  In addition, when connection is made using conductive particles having a relatively small particle size, there is a problem that the conductive particles aggregate and the connection resistance increases due to the aggregated conductive particles.

  The present invention has been made in view of the above circumstances, an adhesive that can be connected in a short time and can suppress an increase in connection resistance due to aggregation, a manufacturing method thereof, and a connection using the adhesive It aims at providing the solar cell module containing a body and its connection body.

  The present inventors have found that by using conductive particles containing a relatively high proportion of particles having a small particle size only in a relatively small amount, the connection resistance is lowered and the thermal conductivity of the adhesive is improved. The present invention has been reached.

That is, the present invention is as follows.
[1] A curable adhesive for electrically connecting a surface electrode conductive wiring of a solar battery cell and a tab wire, including conductive particles and an organic binder, the conductive particles being 0.01 to 1 The adhesive described above, wherein the adhesive is contained in an amount of 0.6% by volume, and the content ratio of the conductive particles of 1 μm or less in the conductive particles is 0.1 to 50% by volume.
[2] The adhesive according to [1], wherein the conductive particles include one or more components selected from copper, silver, nickel, gold, and tin.
[3] The adhesive according to [2], wherein the conductive particles include a silver component and a copper component.
[4] Connection of solar battery cell including surface electrode conductive wiring, tab wire, and cured curable adhesive according to any one of [1] to [3] electrically connecting them body.
[5] The connection body according to [4], wherein the surface electrode conductive wiring has a thickness of 0.01 μm or more and 150 μm or less.
[6] The connection body according to [4] or [5], wherein the surface electrode conductive wiring contains silver, and the tab wire contains copper.
[7] A solar battery module comprising the connection body according to any one of [4] to [6] and a solar battery cell substrate.
[8] The solar cell module according to [7], wherein the solar cell substrate is a silicon, glass, CIGS, aluminum nitride, or sapphire substrate.
[9] A method for producing a curable adhesive for electrically connecting a surface electrode conductive wiring and a tab wire of a solar battery cell, the following steps:
The manufacturing method of the said adhesive agent including the process which makes the organic binder contain 0.01-1.6 volume% of conductive particles whose volume% of 1 micrometers or less of conductive particles is 0.1-50 volume%.

  ADVANTAGE OF THE INVENTION According to this invention, the adhesive for solar cells which can be connected in a short time and can suppress the increase in connection resistance by aggregation, a connection body using the same, and a solar cell module including the connection body Can be provided.

  Hereinafter, modes for carrying out the present invention (hereinafter abbreviated as “embodiments”) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement in various deformation | transformation.

(Curable adhesive)
In the present invention, the adhesive is a curable adhesive for electrically connecting the surface electrode conductive wiring and the tab wire of the solar battery cell, and includes at least conductive particles and an organic binder.

(Curable adhesive-conductive particles)
Among conductive particles conventionally known in this field, the conductive particles preferably have one or more components selected from copper, silver, nickel, gold and tin, and have good thermal conductivity and connection. Those that impart conductivity are preferred. Since such metal conductive particles according to an embodiment of the present invention are harder than conductive particles obtained by metal-coating a resin, the effect of eliminating the organic binder in the adhesive is high, and a relatively small amount. Is preferable because the conductive particles can sufficiently come into contact with each other to provide a stable electrical connection.

  In particular, since conductive particles of 1 μm or less are also used for electrical connection, it is preferable that the surface of the conductive particles has excellent conductivity. Copper-silver component, gold-copper component, gold-nickel component, tin-copper component Conductive particles having are preferred.

  The conductive particles more preferably contain a copper component and a silver component. As a result, in the solar cell module in which the silver surface electrode conductive wiring and the tab wire mainly composed of the copper component are connected via the conductive particles, the components of each wiring diffuse to the conductive particle side at the time of connection due to the concentration gradient. It can be prevented from being eaten.

  The conductive particles containing a copper component and a silver component further preferably contain 10 ppm or more and 10000 ppm or less oxygen, and more preferably contain 5000 ppm or more and 9000 ppm or less oxygen. By containing 10 ppm or more of oxygen, the effect of suppressing the diffusion of silver and copper components into the conductive particles and further preventing biting of the tab electrode mainly composed of the silver electrode conductive wiring and the copper component can be obtained. Moreover, electrical connectivity can be maintained in a favorable state because the oxygen concentration in the conductive particles is 10,000 ppm or less.

  The crystal size of the copper and silver components contained in the conductive particles is preferably 50 angstroms or more and 5000 angstroms or less because a stable conductive connection can be achieved with the silver electrode conductive wiring and the tab wire mainly composed of the copper component. When the thickness is 50 angstroms or more, the crystal grain size becomes a stable connection. By having a crystal size of 5000 angstroms or less, it is possible to prevent the connection points of copper and silver in the conductive particles from being biased to either component.

  The content of the conductive particles of the curable adhesive is preferably 0.01% by volume or more, more preferably 0.05% by volume or more, from the viewpoint of obtaining sufficient electrical bonding. More preferably, it is at least 1% by volume. Moreover, it is preferable that it is 1.6 volume% or less from the viewpoint of obtaining a sufficient bonding area even when connected with a low load, and improving the conduction stability, and more preferably 1.3 volume% or less. Preferably, it is 1.1 volume% or less.

  As the conductive particles, particles having an average particle diameter of 1 μm to 100 μm can be used. The average particle diameter is preferably 1.5 to 50 μm, more preferably 2.0 to 30 μm. The particle shape is not particularly limited to a sphere, pseudosphere, or non-sphere. Moreover, the particle diameter may be mixed. The average particle diameter used here refers to the particle diameter at 50% volume integration.

  Further, in one embodiment of the present invention, the conductive particles used are 1 μm or less of conductive particles from the viewpoint of enabling good connection in a short time by increasing thermal conductivity with fine particles. It is preferable to contain 0.1% by volume or more, more preferably 0.5% by volume or more, more preferably 1% by volume or more, or 5% by volume or more. . The content of conductive particles of 1 μm or less contained in all the conductive particles is preferably 50% by volume or less from the viewpoint of preventing fine conductive particles from agglomerating and unstable connection. , 40% by volume or less, more preferably 30% by volume or less or 20% by volume or less.

  The content rate in which conductive particles of 1 μm or less are included in all the conductive particles is measured as follows.

  For the conductive particles in the adhesive, the volume cumulative distribution of particles of 0.01 to 100 μm is measured with an air flow particle size distribution meter, and the cumulative volume abundance of particles having a size of 1 μm or less in the obtained volume cumulative distribution (volume%) ) As the content.

  As a method for preparing the conductive particles, for example, a predetermined amount of copper, silver, and if necessary, a third component is melted at a high temperature (a temperature higher than the melting point by 100 ° C.) in an inert atmosphere and sufficiently stirred. Thereafter, the molten metal is rapidly solidified while being atomized by blowing helium, nitrogen, hydrogen, or argon gas. Further, chemical methods such as vapor deposition, CVD, sintering, precipitation, plating, and physical methods can be used.

  The average particle diameter of the conductive particles can be controlled by precision classification. The amount of particles of 1 μm or less can also be controlled by a general classification method and mixing the particles.

  Further, when the conductive particles are solidified, a small amount of oxygen is contained in the atmosphere of helium, nitrogen, or argon, so that the conductive particles can have a uniform oxygen concentration. In order to contain an appropriate amount of oxygen in the conductive particles, it is preferable to contain about 0.1% oxygen in the inert atmosphere. Further, by adjusting the supply rate amount of the molten metal and the cooling gas during rapid solidification, the rapid cooling rate can be adjusted and the crystal size of the conductive particles can be controlled.

(Curable adhesive-organic binder)
As an organic binder of the said adhesive agent, it can use individually or in mixture. For example, an organic binder containing at least one selected from an epoxy resin, a polyimide resin, an acrylic resin, a phenoxy resin, a polyester resin, a urethane resin, a polyamide resin, a silicone resin, a modified resin, and the like is preferable.

(Curable adhesive-other components)
A silane coupling agent, an aluminum coupling agent, a titanium coupling agent, a silicone pressure-sensitive adhesive, or the like may be added to the adhesive from the viewpoint of adhesion. Furthermore, dispersing agents for conductive particles, chelating agents for suppressing silver and copper migration, rubber components, thickeners, antifoaming agents, adhesion aids for controlling resin fluidity and film physical properties, etc. These additives may be added.

(Curable adhesive-production method)
As a method for producing the adhesive, for example, conductive particles are dispersed in an organic binder dissolved in a solvent, and additives are mixed there if necessary. These are mixed well to disperse the conductive particles.

  The above-mentioned adhesive remains in a paste form as necessary, or the dispersion is coated and dried to form a film. In the case of a paste, add an appropriate solvent as needed, apply it on the surface electrode conductive wiring or tab wire by printing or dispenser, and connect the surface electrode conductive wire and tab wire by heating, pressing, etc. It is preferable to do.

  The film thickness in the case of forming a film in order to sufficiently cure the resin in a short time is preferably 100 μm or less, more preferably 75 μm or less, and even more preferably 50 μm or less or 40 μm or less. preferable. From the viewpoint of obtaining good adhesive strength, it is preferably 1 μm or more, more preferably 5 μm or more, and further preferably 10 μm or more or 20 μm or more.

  Also, when the thickness is relatively thin (10 μm to 40 μm), in order to make it easy to handle as a film, it is coated and dried on a flexible film having some rigidity such as a polyester film, and the flexible film is peeled off at the time of use. Are preferably used. At this time, an adhesive may be sandwiched between cover films. The film-like adhesive can be produced in units of several m to 1000 m as required.

(Connected body)
In the embodiment of the present invention, the connection body is obtained by curing the curable adhesive and electrically connecting the surface electrode conductive wiring and the tab wire.

(Connector-cured curable adhesive)
The said curable adhesive is hardened | cured and the connection body for photovoltaic cells is formed. The adhesive after curing preferably has an elastic modulus (Young's modulus) at 20 ° C. to 40 ° C. of about 0.1 GPa to 4 GPa.

  The linear expansion coefficient of the cured adhesive is preferably 6 ppm to 200 ppm / ° C., and the water absorption is preferably 0.01% to 5%.

  Moreover, as a hardening method of an adhesive agent, the method of hardening using the hardening reaction or polymerization start reaction by a well-known heat | fever, an electron beam, light, a cation, and a radical as needed is mentioned. When using an epoxy resin as an organic binder to cure the adhesive, it is preferable to use a latent curing agent. When anion, cation, or radical polymerization is used, a known material such as a polymerization initiator, a cation generator, or an anion generator may be used.

  Among them, it is preferable to perform thermosetting, and the heating temperature is preferably 50 to 230 ° C. and the heating time is preferably 1 second to 1 hour from the viewpoint of productivity, and the adhesive is cured by supplying heat with hot air, ultrasonic waves, or a heating head. The method is preferred. At this time, in order to improve the connection of the adhesive, pressurization may be performed at 0.1 MPa to 50 MPa.

(Connector-surface electrode conductive wiring)
In one embodiment of the present invention, the surface electrode conductive wiring contains silver, and preferably consists essentially of silver, but any material can be used as long as it effectively functions as the surface electrode conductive wiring. In one embodiment, the thickness is preferably 0.01 μm or more and 150 μm or less. Moreover, it is preferable that it is 0.01 micrometer or more from a viewpoint of preventing the biting of an electrode, and it is preferable that it is 150 micrometers or less from a viewpoint of making the unevenness | corrugation on the surface of a conductor wiring small. When electrically connecting the surface electrode conductive wiring and the tab wire using the adhesive, the surface electrode conductive wiring is preferably prepared on the substrate in advance.

  The width of the surface electrode conductive wiring is not particularly specified, and can be used with a wide wiring width such as a width of 0.1 μm to 10 mm.

(Connector-Tab line)
In one embodiment of the present invention, the tab wire contains copper, and preferably consists essentially of copper, but any material can be used as long as it functions effectively as a tab wire. The tab wire is preferably coated with a component composed of one or more selected from tin, silver, copper, palladium, indium, and bismuth to prevent the tab wire from being oxidized. For example, a tab line having a thickness of 1 μm to 2000 μm is used.

(Solar cell module)
In the embodiment of the present invention, the solar cell module has one or more solar cells including the solar cell substrate and the connection body, and preferably a plurality of solar cells in series and / or in parallel by the connection body. It has a connected structure.

(Solar cell module-solar cell substrate)
As a substrate for solar cells used in the present invention, crystalline silicon, single crystal silicon, amorphous silicon, cadmium-tellurium, CIGS, sapphire, glass, ITO, IZO, gallium, aluminum nitride, boron nitride, glass epoxy, polyimide And a transparent or non-transparent substrate.

  Next, the present embodiment will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples.

  The physical properties of the prepared conductive particles were measured by the methods shown below.

(1) Average particle diameter of conductive particles, and volume% of 1 μm or less in conductive particles
Average particle diameter: The volume integrated average value was measured with a laser diffraction measuring instrument HEROS & RODOS SR type, and the particle diameter when the volume integrated was 50% was defined as the average particle diameter value.
Volume% of conductive particles of 1 μm or less in all conductive particles: Volume integrated% of 1 μm or less of the volume integrated distribution of conductive particles determined by the laser diffraction type measuring device was determined.

(2) Metal composition of conductive particles Table 1 shows the conductive particle composition, average particle diameter, and volume% of 1 μm or less in all conductive particles.

<Examples 1-5>, <Comparative Examples 1-2>
The adhesive compositions in the ratios shown in Compositions 1 to 4 and 6 to 9 in [Table 2] were dissolved in an ethyl acetate solvent at a concentration of 50% by mass, applied onto PET having a thickness of 50 μm, and 60 ° C. in air. After drying for 10 minutes, the solvent of ethyl acetate was removed, and a film adhesive having a thickness of 35 μm was prepared. Moreover, the adhesive composition of the ratio shown to the composition 5 was melt | dissolved in the ethyl acetate / toluene solvent by the density | concentration of 50 mass%, and the paste-form adhesive was created.

The following organic binders were used for the adhesive.
a. Bisphenol A type epoxy resin (AER2600 manufactured by Asahi Kasei Chemicals Corporation)
b. Bisphenol F epoxy resin (RE-303S manufactured by Nippon Kayaku Co., Ltd.)
c. Naphthalene type epoxy resin (HP-4032D manufactured by Dainippon Ink Co., Ltd.)
d. Dicyclopentadiene type epoxy resin (HP7200 manufactured by Dainippon Ink Co., Ltd.)
e. Bisphenol A type phenoxy resin (PKHC manufactured by InChem Corporation (Rock Hill, SC, USA))
f. Polyol-modified phenoxy resin (PKHM301 manufactured by InChem Corporation (Rock Hill, SC, USA))
g. Latent curing agent (HX3941HP microcapsule type imidazole (latent curing agent) manufactured by Asahi Kasei Epoxy Co., Ltd.)
h. Silane coupling agent (Shin-Etsu Chemical Co., Ltd. KBM403)
i. Silicone adhesive (SD4580 manufactured by Toray Dow Corning Co., Ltd.)

<Connection test (when connected for 10 seconds)>
The connection body was created as follows using the film adhesive of each composition. The adhesive was lightly affixed on the silver surface electrode conductive wiring of the base material shown below, and then the adhesive was peeled off from the PET film. The tab wire having the copper component shown below is faced to the surface electrode conductive wiring to which the adhesive is adhered, and the tab is bonded at 180 ° C. for 10 seconds and 1.7 MPa using a 1.5 mm heating head. The wire was cured by heating and pressing.

  Moreover, the connection body was created as follows using the paste adhesive of each composition. First, the paste was applied onto the silver surface electrode conductive wiring by a dispenser, printing or the like. Next, the tab wire having the copper component shown below is faced to the surface electrode conductive wiring coated with the adhesive, and using a 1.5 mm heating head, the conditions are 180 ° C. and 2.5 MPa for 10 seconds. The connection time was cured by heating and pressing the tab wire.

<Connection test (when connected for 3 seconds)>
A connection test was performed under the same conditions except that the connection time was changed from 10 seconds to 3 seconds using a film-like or paste-like adhesive of each composition.

  The connected body thus obtained was subjected to a performance test by the following method. The results are shown in Table 3.

(Substrate having surface electrode conductive wiring)
Base material 1: Silver wiring (10 μm thickness, 100 μm width) printed on a crystalline silicon substrate Base material 2: Silver wiring (2 μm thickness, 200 μm width) printed on an amorphous silicon substrate Base material 3: Single crystal silicon substrate Printed with silver wiring (50 μm thickness, 300 μm width) Base material 4: printed with silver wiring (140 μm thickness, 300 μm width) on CIGS substrate Base material 5: silver wiring (0.5 μm thickness, 300μm width) printed

(Tab line)
Wiring 1: Copper wire (200 μm thickness) coated with Cu—Sn—Ag Wiring 2: Copper wire (100 μm thickness) coated with Sn—Pb Wiring 3: Copper wire (300 μm thickness) coated with Sn—Ag Wiring 4: Copper wire (300 μm thickness) coated with Sn-Ag-Bi-In

<Performance test method>
1. Reliability evaluation of connection resistance when connected for 10 seconds and reliability evaluation of connection resistance when connected for 3 seconds Using a Hioki 9455 type multimeter, reliability test of connection body (3000 hours at 85 ° C. and 85% RH) The resistance between the surface electrode conductive wiring and the tab wire after standing for a long time was measured by a four-terminal method.

Judgment criteria (same when connected for 10 seconds and connected for 3 seconds)
Connection resistance value R after reliability test
A: R <20 mΩ, B: 20 mΩ ≦ R <50 mΩ, X: 50 mΩ ≦ R

<Judgment method of aggregation>
100 aggregated particles in the adhesive at the time of connection were randomly extracted and observed with an optical microscope at a magnification of 100 to determine the aggregability of the conductive particles contained in the used adhesive.
A: When the average particle size is agglomeration of less than 3 times the average size ○: When the agglomeration is an average particle size of 3 times or more and less than 10 times the average particle size ×: Average When the average particle size is more than 10 times larger than the particle size

  As shown in Table 3, the connection body manufactured by the manufacturing method of each example can obtain a stable connection resistance after the reliability test even when connected in 3 seconds, and according to the manufacturing method of each comparative example. It was confirmed that the manufactured connection body had high connection resistance after the reliability test when connected in 3 seconds.

  By using the adhesive of the present invention, it is possible to provide a solar battery cell that secures stable conduction even in a short-time connection and a solar battery module using the solar battery cell.

Claims (9)

  A curable adhesive for electrically connecting a surface electrode conductive wiring of a solar battery cell and a tab wire, comprising conductive particles and an organic binder, the conductive particles being 0.01 to 1.6 volume And the content ratio of the conductive particles of 1 μm or less in the conductive particles is 0.1 to 50% by volume.   The adhesive according to claim 1, wherein the conductive particles include one or more components selected from copper, silver, nickel, gold, and tin.   The adhesive according to claim 2, wherein the conductive particles include a silver component and a copper component.   The connection body of a photovoltaic cell containing the curable adhesive as described in any one of Claims 1-3 which hardened | cured the surface electrode conductive wiring and the tab wire, and electrically connected them.   The connection body according to claim 4, wherein the surface electrode conductive wiring has a thickness of 0.01 μm or more and 150 μm or less.   The connection body according to claim 4, wherein the surface electrode conductive wiring contains silver, and the tab wire contains copper.   The solar cell module which has the connection body as described in any one of Claims 4-6, and a photovoltaic cell board | substrate.   The solar cell module according to claim 7, wherein the solar cell substrate is a silicon, glass, CIGS, aluminum nitride, or sapphire substrate. A method for producing a curable adhesive for electrically connecting a surface electrode conductive wire and a tab wire of a solar battery cell, the following steps:
The manufacturing method of the said adhesive agent including the process which makes the organic binder contain 0.01-1.6 volume% of conductive particles whose volume% of 1 micrometers or less of conductive particles is 0.1-50 volume%.